The present invention pertains to percussive soil compacting tools and, more particularly, to vibration isolation in a manually operated percussion rammer.
Percussion rammers are well known in the construction industry and are used to compact soil and other loose materials in a variety of construction and excavation operations. Such devices are typically manually operated by a single operator. A percussion rammer is distinguishable from a vibration compaction device in terms of both amplitude and frequency of operation. A rammer may operate with a vertical amplitude in the range of 2-3 inches (about 50-75 mm) and a frequency of about 600-800 cpm. A vibratory compactor, on the other hand, has a much smaller amplitude, for example, 0.060 inch (about 1.5 mm) and a much higher frequency, for example, 4,000-6,000 cpm.
A typical percussion rammer thus provides a generally vertically oriented, large amplitude movement to a flat soil engaging shoe that compacts the soil with a pounding type of movement. The compacting shoe is typically mounted with its flat surface at an angle slightly less than 90xc2x0 to the vertical and, as a result, the operating axis along which the percussive tamping movement is transmitted is slightly forwardly-inclined. The angle of operating movement may be, for example, 15xc2x0 to the vertical. This angled orientation results in a forward component of motion with every stroke and permits the operator to guide the machine in a forward operating path over the surface by grasping a horizontal operator handle at the rear of the machine. The operator handle is typically attached to the rear of a frame that includes two generally horizontal laterally spaced components that are attached by their opposite forward ends to a cushioning pivot mechanism near the upper end of the operating axis. The cushioning pivot arrangement typically comprises a pair of large elastomeric elements interposed between the forward ends of the lateral frame members and the body of the machine, so the frame and operator handle may pivot vertically relative to the rammer as it moves up and down. This arrangement helps isolate the generally vertical component of operating movement from the operator handle and the hands of the operator grasping the handle. However, because of the inclined orientation of the operating axis of the machine, there is a significant horizontal component of movement that the torsional mounting of the side frame to the machine does little to damp or isolate. This horizontal component of movement is thus transmitted directly through the side frame members to the operator handle and the hands of the operator.
Recently, worker safety regulations worldwide have examined the effects of hand/arm vibration levels in manually operated vibratory equipment. Some jurisdictions have effected regulations that apply measured vibration levels to operating time to make sure that operators are given periodic rests while using such equipment. Of course, if vibration levels can be lessened or eliminated, operator time may be increased or the rest periods may be decreased. In any event, eliminating or lessening the horizontal component of percussion rammer operating movement would be a benefit to the machine operator.
In a basic embodiment of the present invention, an operator handle assembly is provided for a percussive soil compacting device to isolate generally horizontal components of operating movement from the hands of the operator, the assembly including a main frame attached at one end to the compacting device, and a manually engageable operator handle attached to the other end of the main frame with a shock absorbing mount oriented to absorb generally horizontal components of operating movement. In a presently preferred embodiment, the main frame includes a pair of laterally spaced frame members having ends adjacent the operator handle and the operator handle includes a generally horizontal manually engageable member having opposite lateral ends; the shock absorbing mount comprises a pair of torsionally resilient shock absorbers each of which is attached with a first connector to an end of said frame member and with a second connector to a lateral end of the operator handle, the first and second connectors oriented to position the shock absorbers on a common torsional axis that is vertically offset from and generally parallel to the horizontal member.
The shock absorbers preferably comprise elastomeric elements, each element being mounted between said first and second connectors. In a preferred embodiment, the elastomeric elements are generally cylindrical and are mounted with their axes on the common torsional axis. In a particularly preferred embodiment, the horizontal member of the operator handle is mounted above the torsional axis.
In the operator handle assembly of the present invention, one end of the main frame is attached to the compacting device with a shock absorbing arrangement that is oriented to absorb generally vertical components of operating movement in a known manner. In an alternate embodiment of the invention, the shock absorbing mount for the operator handle comprises a pair of linear shock absorbers, each of which interconnects an end of a horizontal frame member and an end of the horizontal operator handle member to dispose the linear shock absorbers in a generally horizontal orientation aligned with the horizontal components of operating movement.
The present invention also encompasses a method for isolating generally horizontal components of operating movement in a manually operated percussive soil tamping apparatus from the operator, comprising the steps of (1) providing a generally horizontal operating handle member with opposite lateral ends, (2) providing a frame with a pair of laterally spaced generally horizontal frame members having ends adjacent the lateral ends of the handle member, and (3) connecting the ends of the handle member to the ends of the frame member with shock absorbing devices oriented to absorb generally horizontal components of operating movement and to minimize transmission thereof to the handle member. In the preferred method, the shock absorbing devices comprise a pair of torsionally resilient shock absorbers, and the connecting step comprises the step of mounting said shock absorbers on a common torsional axis vertically offset from and parallel to the operating handle member.